Seasonal Outlook Interpretation

The Seasonal Hurricane Outlook

The seasonal hurricane outlook is part of a long-term research project pioneered by tropical research meteorologist Dr. William Gray at the Colorado State University. Each year, both before and during the hurricane season, Dr. Gray and his colleagues at Colorado State release their most recently updated seasonal hurricane outlooks to the public.

Outlooks are issued for the number of named storms, hurricanes, and major hurricanes (Category-3 or above) in a season, as well as for the number of named storm days, hurricane days, and major hurricane days. "Named storms" include hurricanes, tropical storms, and subtropical storms. The seasonal outlook is issued six times each year: in December and April prior to the upcoming season, and in June, August, September, and October during the hurricane season.

The numbers released in these outlooks are not meant to be taken literally. The outlooks are experimental, their meteorological and oceanographic predictors are continuously evolving, and their skill varies depending on the month in which they are issued. Whether a particular seasonal outlook is successful may be judged based on whether its predictions are on the correct side of (above or below) an average season.

An average season (rounded to the nearest integer) consists of 10 named storms, including 6 hurricanes, itself inclusive of 2 major hurricanes. If the numbers in the outlook project a below-average season, and a below-average season is later observed, that is an example of a successful seasonal outlook. The seasonal forecasters judge their own skill level based on their ability to produce better results than could be obtained by looking at climatological data alone; they have discovered that their outlooks do provide quite a bit more information about the upcoming season than could be derived solely from climatology.

The seasonal outlook makes use of the knowledge bases of a multiple number of sciences, including meteorology, climatology, and oceanography to make its predictions. Because it extends well beyond present-day forecast lead times for weather forecasting and its associated models, it may be thought of as a kind of extended outlook. It uses statistical methods for its predictions, whereas the daily weather forecast, including the hurricane forecast, uses current meteorological data projected forward in time.

The seasonal outlook is based not on the day-to-day changes in the state of the atmosphere, but on the current states of recognizable atmospheric and oceanic features and cyclical phenomena lasting longer than that. Recognizable features may include wind, pressure, and sea surface temperature anomalies and/or gradients, together with the longer-range phenomena that help shape them, some of which change their states in cycles of months, years, or even decades, and which have effects on a global scale. Such features and cyclical phenomena, when observed to be in particular places or in particular states during certain times of year, have been found to be statistically correlated with relatively active or inactive hurricane seasons, and it is these correlations that are used to make the forecasts.

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